Basic ScienceAging changes in lumbar discs and vertebrae and their interaction: a 15-year follow-up study
Introduction
Many studies have focused on either the intervertebral disc, as it is believed by many to be a culprit in back pain problems, or the vertebral body, typically related to osteoporotic fracture or Modic changes, but very few studies have examined both the structures and their relation. Several investigations of lumbar vertebral bone mineral density (BMD) in relation to disc degeneration have been conducted, with most suggesting that higher vertebral BMD is associated with more disc degeneration [1], [2], [3]. Analyses of autopsy material, using estimates of disc degeneration from discography and vertebral BMD from microcomputed tomography, showed more specifically that higher BMD of the vertebral body and greater end plate thickness were associated with more disc degeneration [4]. Based on another study of 27 cadavers, Simpson et al. [5] hypothesized that disc “disorganization significantly modulates bone degeneration that could influence the incidence of vertebral body crush fracture.” Moore at al [6] found in a study of sheep that “outer anular injury” was associated with greater vertebral trabecular bone volume. Overall, these studies suggest an interaction between the degeneration or pathogenesis of discs and vertebrae, but longitudinal studies are needed to clarify these relations and others. A number of investigators have conducted longitudinal studies of disc herniations after surgery, “Modic changes” [7], [8], or qualitatively assessed disc degeneration [9]. Yet, we are aware of no longitudinal studies that investigate the concurrent changes in morphology of the discs and vertebrae and their interaction.
Better understanding of pathogenesis has commonly enhanced prevention and led to more rational treatment of underlying illnesses. Our goals were to describe the changes in shape and size of lumbar vertebrae and discs occurring over a 15-year period in a general population sample of men using quantitative magnetic resonance imaging (MRI) measures and visual assessments.
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Subjects
Participants for this study were selected from the 232 monozygotic (MZ) twins initially recruited in the Twin Spine Study, which were drawn from the population-based Finnish twin cohort that included all same-sex twins born in Finland before 1958 and still alive in 1975 [10]. The initial selection of MZ twins, which has been described in detail previously [10], was based on co-twin discordance for one of the common environmental exposures, primarily occupational or leisure physical activities.
Vertebra changes based on quantitative measures
After 5 years, the vertebra height and width increases (0.4% and 0.4% mean increases in the upper lumbar discs and 0.2% and 0.1% in the lower discs, respectively) were not statistically significant (Table 1). Over 15 years, however, the vertebra heights increased in mean by 3.1% (0.8 mm) in the upper lumbar levels and by 4.7% (1.1 mm) in the lower lumbar levels (p<.001, respectively). The largest increases in mean upper and lower vertebra heights were 8.6% (2.0 mm) and 16.8% (3.5 mm; Fig. 2,
Discussion
Lumbar disc height decreased over a 15-year period by approximately 9% to 10% on an average in the upper lumbar region and 12% to 13% in the lower lumbar discs in our population-based sample of middle-aged men, but the variations observed among individuals were large. Some had no apparent progression of disc degeneration, whereas others had dramatic disc height loss. The surprising finding, however, was a mean increase in the lumbar vertebra height that was associated with adjacent disc height
Conclusion
While discs and vertebrae appear to change in concert, the finding of increased vertebra height awaits replication.
Acknowledgments
Supported by the NIH NIAMS; The Work Environment Fund, Finland; The Alberta Heritage Foundation for Medical Research, Canada; and the Canada Research Chairs Program.
The authors thank Dr. JDG Troup for his helpful comments and suggestions.
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Author disclosures: TV: Nothing to disclose. MCB: Nothing to disclose. LEG: Consulting fee or honorarium: University of Alberta (A) KG: Nothing to disclose.
The disclosure key can be found on the Table of Contents and at www.TheSpineJournalOnline.com.